CODEWITHSUNDEEP
c#formsbackgroundworkerfreeze
alexD
alexD

Reputation: 2364

BackgroundWorker might be causing my application to hang

I have a Form that uses a BackgroundWorker to execute a series of tests. I use the ProgressChanged event to send messages to the main thread, which then does all of the updates on the UI. I've combed through my code to make sure I'm not doing anything to the UI in the background worker. There are no while loops in my code and the BackgroundWorker has a finite execution time (measured in seconds or minutes). However, for some reason when I lock my computer, often times the application will be hung when I log back in. The thing is, the BackgroundWorker isn't even running when this happens. The reason I believe it is related to the BackgroundWorker though is because the form only hangs when the BackgroundWorker has been executed since the application was loaded (it only runs when given a certain user input).

I pass this thread a List of TreeNodes from a TreeView in my UI through the RunWorkerAsync method, but I only read those nodes in the worker thread..any modifications I make to them is done in the UI thread through the progressChanged event.

I do use Thread.Sleep in my worker thread to execute tests at timed intervals (which involves sending messages over a TCP socket, which was not created in the worker thread).

I am completely perplexed as to why my application might be hanging. I'm sure I'm doing something 'illegal' somewhere, I just don't know what.

Upvotes: 1

Views: 1984

Answers (3)

Gordon
Gordon

Reputation: 1

Sounds like the dreaded UserPreferenceChanged event problem where a ui component has been created on a background thread without a message pump. The main ui thread synchronously sends the event to all registered ui windows and will hang because the ui component on the background worker thread is unable to process the UserPreferenceChanged event.

Upvotes: 0

alexD
alexD

Reputation: 2364

Well, this one is old but it turned out that the problem was completely unrelated to my code. Due to recent changes in our software, the amount of logging had increased exponentially and our log buffer was overflowing causes the application to crash. It was just a coincidence that this was happening at the same time that I was working on this specific piece of code. In any case, I still made sure that I wasn't doing any operations on UI elements from a BackgroundWorker, even if it was as trivial as checking/unchecking a TreeNode.

Upvotes: 1

to StackOverflow
to StackOverflow

Reputation: 124696

I pass this thread a List of TreeNodes from a TreeView in my UI through the RunWorkerAsync method, but I only read those nodes in the worker thread.

By "only read" I assume you mean "only access property getters". But property getters can execute code that you don't control - for example TreeNode.IsSelected will call a native method and send a Windows message (take a look with Reflector).

Instead you should extract the data you need from the TreeView in the UI thread and pass it to the background worker. Not only will you avoid this problem, but your design will be more loosely coupled.

Upvotes: 1

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